1. Field of the Invention
The present invention generally relates to a pulse rate monitor and, more particularly, to a device for monitoring the rate of human heart beating and for providing an indication when the heart beats at a rate which is outside a rate range, defined by limits, which are programmable into the device from an external source.
2. Description of the Prior Art
As is appreciated, during each systolic heart beat the heart contracts, forcing blood through the arteries, in the course of which the arteries expand. This expansion can be sensed either manually or by means of sensing devices at various points in the body. Typically, it is sensed at the wrist, or at the carotid artery at the neck. Various devices have been proposed in the prior art to measure or monitor the human body heart beat rate, which is generally expressed in terms of beats or pulses per minute.
In the devices, proposed to measure the heart beat rate, various means have been proposed to automatically sense the heart beats by sensing the expanding arteries. These means include pressure transducers, photoelectric devices, mechanical diaphragms and the like. The sensed heart beats are typically converted into corresponding electrical pulses whose rate is monitored. Some presently known heart beat monitors provide an indication whenever the heart beat rate is outside a rate defined by high and low rate limits, which are manually set in the monitor.
The use of a heart beat monitor, capable of providing an indication when the heart beat rate exceeds and/or falls below selected rate limits is particularly important for a patient having questionable cardiac conditions, e.g., a patient with a cardiac stimulator. By presetting the heart beat monitor with high and low rate limits, chosen to be above and below the patient's pacemaker pulse rate, or the patient's normal pulse rate, the heart beat monitor can be used to indicate pacemaker failure or excessive pulse rate above a normal rate.
The heart beat monitor, particularly one with a preset upper limit can be used very effectively for post heart attack patients. Generally, doctors advise such patients to exercise in order to strengthen their heart muscles. However, when exercising it is most important that the weakened heart muscles not be overtaxed. This can be achieved by first setting the high or upper limit in the heart beat monitor to a selected relatively low level, and permit the patient to first exercise until his heart beat rate reaches the set limit. Then, as the patient's condition improves the upper limit may be raised. Since practically all post heart attack patients are under a doctor's care, it is of primary importance to enable the doctor, rather than the patient, to establish the limits in the heart beat monitor, based on the medical diagnosis of the patient's conditions.
In the prior art, heart beat monitors have been described which are in the form of a wristwatch intended to be worn by the patient. Some of these monitors include means which enable the patient to set and vary the upper and lower limits by manipulating dials or other means in the monitor. This is, the limits are subject to change by the patient rather than the doctor, and therefore may be set at unsafe levels for the particular patient condition. A need therefore exists for a heart beat monitor in which the limits are programmable or storeable into the monitor from an external source under the control of a doctor or the like. Once the limits are stored they should not be subject to variation by the monitor-wearing patient, except by a subsequent programming operation, from the external source. Such a monitor would prevent the patient from setting improper limits in the monitor.
In such an externally programmable monitor it is highly desirable to store the limits so that they remain unaffected by the monitor's main power source, e.g., a primary battery, which may be depleted by energization of the various monitor circuits including an audible alarm and/or a visual rate display.